1. Field of the Invention
This invention relates to a rotor of a canned motor for a canned motor pump, which performs rotation through electromagnetic interaction with a stator.
2. Description of the Prior Art
A canned motor pump having a canned motor mounted therein is generally of the type shown in FIG. 1 of the accompanying drawings, in which the motor is disposed at one side of the pump. The motor comprises a rotor 3 includes a core assembly having a plurality of stacked cores, and a rotary shaft 1 for rotating an impeller the shaft being 5, press-fitted into the central portion of the core assembly. The motor also included a stator 2 disposed peripherally of the rotor 3 in radially facing relation to the rotor, whereby the rotor 3 performs high speed rotation by electromagnetic interaction with the stator, so that a impeller 5 secured to one end of the rotary shaft 1 therewith is rotated, thereby pumping fluid.
Bearings 4 guide and support the opposite end portions of the shaft 1. Lubrication of the sliding contact surfaces between the rotary shaft 1 (which rotates at high speed) and bearings 4 is not provided by supplying separate lubricating oil; instead, the fluid that is being pumped is circulated into the interior of the motor portion. Therefore, the rotor of the motor for the canned motor pump must be arranged to meet the requirements of airtightness, preventing the fluid from permeating into the interior of the rotor and avoiding corrosion thereof.
To satisfy the requirements set forth above, the prior rotor employs the construction shown in FIGS. 2 and 3 of the accompanying drawings. A core assembly 3a includes stacked cores 6 each having a central aperture and a plurality of circumferentially spaced slots 10 formed thereon. Opposite end rings 8a and 8b (copper plates) are attached to the opposite sides of the core assembly, each end ring having a central aperture and slots corresponding to the central aperture and slots of the core. Copper wires or bars are inserted into the slots 10 and secured to the end rings 8a and 8b by welding. A a rotor can 9 of stainless material is disposed on the outer peripheral surface of the core assembly to enclose it, and the rotary shaft is 1 press-fitted into the central aperture of the combination of the core assembly and the end rings. Accordingly, permeation of fluid into the core assembly 3a comprising the cores 6 is prevented by the end rings 8a and 8b and the rotor can 9, which entirely surround the core assembly.
In this prior rotor, the end rings and rotor bars, which serve as rotor conductors, are made of copper, which increases the manufacturing cost of the product. Moreover the processes of inserting the rotor bars into the slots of the core assembly and then welding the bars to the end rings complicates the mannfacturing operation, thereby lowering productivity. In addition, since the rotor can which encloses the core assembly to prevent permeation of water from the outside is made of separate stainless material, the manufacturing cost is increased. Furthermore, the thickness of the rotor can itself increase the gap between the rotor and the stator by at least 0.2 mm, thereby lowering the efficiency of the motor. Moreover, even if the rotor can has ben accurately finished and mounted around the core assembly, the airtightness between the rotor can and the core assembly may not be properly maintained with use of the motor for a long time, resulting in permeation of the core assembly.